Field of the Invention
The present invention relates to the arrangement of pipes for geothermal heat exchange and in particular to arrangements of a plurality of pipes twisted onto a central conduit for geothermal heat exchange.
Description of the Related Art
Geothermal heat exchange structures are well known and include a broad array of configurations for the exchange of heat between an environmental conditioning device and the earth. An idealized example of an environmental conditioning system with a geothermal heat exchanger is shown in FIG. 1. The environmental conditioning systems defined herein include a geothermal heat exchanger that provide environmental conditioning for a structure 2 using an environmental conditioning apparatus such as a heat pump or other similar device 4 that is in fluid communication with a pipe 5 that contains a liquid for the transfer of heat. Pipe 5 is a geothermal heat exchanger positioned in a hole 6 in the ground 8. Pipe 5 can be a single loop, a single pipe with multiple branches, a coaxial pipe and multiple pipes depending upon the desired construction of the geothermal heating system.
Environmental conditioning apparatus or heat pumps 4 that use geothermal heat exchangers are commonly identified as heating and cooling systems. Geothermal heat pumps 4 are known for their superior performance in delivering energy conserving heating and/or cooling to homes, industrial buildings and residential and industrial complexes in many climates. As defined herein, environmental conditioning apparatus include heating, cooling and combined heating and cooling systems. See, for example, http://www.igshpa.okstate.edu/geothermal/geothermal.html; www.summitmechsystems.com/pages/3.1.html; www.renewableheating101.com/geothermal/loops; http://minnesotageothermalheatpumpassociation.com/geothermal/earth-loop-options/; and http://www.informedbuilding.com/Geothermal/Main16/Types-of-Geotherm.
However, a barrier to the wide spread use of geothermal heat exchangers is the high cost of installation of pipe 5 ground loops that provide the essential heat transfer from the heat exchange liquid that is circulated through pipes 5 to the earth 8. Also, the presently available ground-loop pipes 5 are limited in many instances in their ability to efficiently utilize vertical boreholes 6 and exchange heat with the earth.
Different geothermal heat exchangers have attempted to overcome these efficiency limitations. The aforementioned websites discuss the various ground loop technologies. Examples of commonly used ground loop technologies include the following: horizontal ground loops, vertical ground loops, and slinky coil ground loops. The slinky coil ground loop is a variation of the horizontal ground loop and it too requires a substantial amount of horizontal land as do other horizontal ground loops. Vertical loops include multiple pipe vertical loops that use less horizontal land, but their structural configurations and relationship to the borehole still limit heat transfer.
Ground loops are usually required to be at least partially grouted as part of their installation. Horizontal and/or multi-angled boreholes can also require grouting. While the thermal or heat transfer coefficients of grouts vary, it is preferred to grout the entire borehole of vertical installations. The goal is to preclude voids in the grout that reduce the efficiency of the heat transfer. The standard practice is to insert a grout pipe all the way to the bottom of the bore and fill the borehole from the bottom up. This process also displaces any water that has pooled at the bottom of the borehole. The grout pipe, however, takes up space in the borehole and can be difficult to insert into the borehole as it has a tendency to catch on irregularities in the surface of the wall of the borehole as well as the pipes. Further installations that only provide bottom to up grouting through a tremie are vulnerable to the creation of voids in and around the arranged pipes and clamps.
When multiple pipes 5 are closely arranged for geothermal heat exchange, it is known that spacing the pipes enhances the heat transfer by increasing the heat transfer surface area. Methods of keeping adjoining pipes separated include the use of headers, footers and clips, in various forms that position individual pipes 5 relative to one another, a tremie type pipe and/or the wall of the borehole. Some multiple pipe configurations include secondary branches that define loops. These branched structures join branches using extended rigid connectors that are known as headers and footers that divide and/or connect pipes 5 in fixed spaced separation relative to one another. Headers and footers, however, take up an excessive amount of horizontal and/or in particular vertical space in the earth which undesirably increases time and cost for installation.
Clips and springs and even headers and footers, keep the pipes separated and oriented advantageously where the pipe is close to objects. Problems arise, however, because the Clips are typically installed every 10-20 feet and between the clips the pipes are not controlled and can maneuver themselves into undesirable positions away from the borehole wall. Clips have some advantages in potentially fixing the position of pipes 5 relative to one another, a tremie pipe or the borehole in proximity to the clip, but clips require manual positioning prior to installation and take up valuable space within the borehole. The taking of excessive space in the borehole can undesirably reduce the quantity and/or size of pipes 5 in the borehole and complicate the use of a tremie pipe and/or grouting due the position of the clips extending transverse to the alignment of the borehole. Headers, footers and clips also limit the flexibility of arranging pipes 5 in that the ability to add or remove one or more pipes can be burdensome and require the changing of headers and/or footers as well as the type of clip installed on pipes 5.
It is also known that geothermal heat exchange applications using straight and/or rigid pipes have multiple limitations that include transportation and manual labor required to connect and then install the one or more straight pipes 5. Coaxial pipes are typically straight pipes with thicker walls that structurally support and maintain the relative position of the inner walls of the pipe that separate the inflow and outflow. The thickness of walls of coaxial pipes undesirably decreases the heat exchange properties of those pipes. Further straight pipes 5 require the creation of turbulent flow in order to achieved preferred rates of heat transfer or exchange. This requires the insertion of mechanical interruptions in the interior of pipe 5 such as undulations and/or vanes that deflect and/or interrupt the flow in pipe 5 to create turbulent flow in pipe 5 with elevated Reynolds numbers and enhanced heat transfer. The creation of turbulent flow is commonly created through high flow rates of the heat exchanging fluid within pipe 5 and can result in undesirable increased power consumption of the overall system.
Heretofore there has not been a high efficiency compact and flexible arrangement of a plurality of pipes for geothermal heat exchange. The geothermal heat exchange apparatus includes a twisted, approximately parallel and spaced arrangement of individual pipes of a plurality of pipes around a central conduit. The geothermal heat exchange apparatus is flexible and can be compactly coiled for storage and transportation as a complete assembly and then readily installed in a borehole. The twist of the plurality of pipes controls the position of each pipe of the plurality of pipes ensuring contact with the center conduit and establishing each pipe of the plurality of pipes in an approximately fixed spaced relation relative to the other pipes of the plurality of pipes.